Analog-to-digital converter



Sept 19, 1957 s. A. PRocTER ANALOG-TO*DIGITAL CONVERTER Filed Feb. s, 1964 QW WW Nw WW Q Im United States Patent Oflice 3,343,156 Patented Sept. 19', 1967 3,343,156 ANALOG-TO-DIGITAL CONVERTER Samuel A. Procter, Minneapolis, Minn., assignor of olle-half to Fred M. Sweet, Minneapolis, Minn. Filed Feb. 3, 1964, Ser. No. 341,863 6 Claims. (Cl. 340-347) This invention relates to the field of code converters and more particularly to an analog-to-digital converter.

Certain types of equipment such as signs which are generally displayed outside of institutions such as banks, saving and loan associations, etc., displaying time and temperature require a form of analog-to-digital converter to convert quantities such as time and temperature from their physical quantities into digital or readable quantities. Since the temperature to be displayed is generally not required to be more than one-half (1/2) of a degree F. in accuracy, the general device used to provide the temperature is a bimetal strip or similar device and thus if the temperature is displayed every five or ten seconds, the shaft input to the code wheel which may be used with the analog-to-digital converter may be somewhere between two temperatures and thus if allowed to remain at such a position, an ambiguous signal would be translated and an improper temperature would most likely be displayed. The present invention provides magnetic means for locking the input device to a particular position to dominate any ambiguous reading.

Furthermore, in devices of the type just described, simplicity and reduction of parts is an absolute essential for simple and reduced maintenance. The matrix employed in the present invention makes use of transistors and a plurality of impedance circuits which are connected in such a manner that with a combination of inputs, changing one at a time, an output may be obtained in decimal or other ycode units.

It is therefore a general object of the present invention to provide an improved analog-todigita1 converter.

It is a more speciiic object of this invention to provide means for magnetically locking the movement of an analog device during the period the code pattern is being read It is still another object of this invention to provide new and novel means for reducing the number of components required to convert coded information into numbers of a given mathematical base.

A more specific object of the present invention is to provide a translator of novel design for converting a code of N bits into a decimal output.

It is still another object to provide a circuit using a plurality of impedances, which when added into a transistor stage representative of a number to a given base, produces output signals representative of the input signals but of a diiferent mathematical base.

These and other objects and advantages of my invention will more fully appear from the following description, made in connection with the accompanying drawings, wherein like reference characters refer to the same or similar parts through the several views, and in which:

FIG. 1 is a schematic diagram of the analog-to-digital converter showing the detection means and code matrix for translating a code; and

FIG. 2 is a diagrammatic view of the magnetically locking device used with the code wheel of the detection means.

In FIG. 1, an analog device 10 is shown connected to a code Wheel 11 and an indexing wheel 13 through a shaft 12. Analog device 10 is a condition responsive device and may consist of a clock or may be a device which is sensitive to temperature, either of which causes rotation of an output shaft. Analog device 10 is of a general character and may be of the bi-metallic spiral type, the bourden tube, bellows, DArsonval movement device, etc. Code Wheel 11 is of the conventional type and is generally formed of a plastic material 14 which is optically clear and formed thereon in concentric circular patterns are a plurality of cut-away or blank spaces 1S formed in a mask 16 to produce a particular code pattern. While it will be apparent that for the purposes of describing the present invention, an optical system is being used, it should also be quite clear that other forms of code patterns and detection equipment may be used. Situated between a lamp 17 and code wheel 11, is a condensing lens 20 which condenses the light from lamp 15 so that the proper beam width is determined and the light is allowed to pass through the slots or cut-away portions 15 of mask 16. A reilector 21 situated behind lamp 17 also aids in conducting the light towards the code wheel.

A number of light sensitive activated switches are contained in an optical scanner 22 where each of the light sensitive devices are identical to each other. One such device is the High Sensitive Light Activated Switch, L7 series which is presently being sold and manufactured by the General Electric Company. This particular device acts in the same manner as an electronic switch when light impinges upon the sensitive element contained therein. For the purposes of illustration in the description of this invention, it will be understood that while the units devices are shown connected to an electrical matrix, those marked 10's and 100s would be connected in like manner and to simplify the description of the invention further, those light sensitive switches working with the units input are designated A, B, C, and D.

The indexing Wheel 13 which is mounted upon shaft 12 has teeth formed therein which are spaced at the smallest increment that is to be read out by the system. For example, a wheel having teeth will permit the code wheel 11 to be indexed every two mechanical degrees and consequently will produce a reading within plus or minus one mechanical degree. A Wheel having 720 teeth will permit index readings and increments. of plus or minus one-half a mechanical degree. It is therefore necessary to determine the degree of accuracy to which the temperature may be required for display and thus determine the number of teeth tobe used in the indexing wheel. An electromagnet 23 has a pole piece 24 which protrudes from the electromagnet and the general contour of the pole piece is such that the face provided at the end of the pole piece is of approximately the same area as the end of a tooth on the index wheel 13. There is also an air gap between the teeth of index wheel 13 and the end of pole piece 24. Thus when current is applied to electromagnet 23, the magnetic iield is formed between pole piece 24 and the teeth on indexing wheel 13, or more specifically to the closest tooth of the` wheel and thus the electromagnet, through the pole piece, locks the index wheel to the nearest incremental position. In order to produce this result, a pulse generator 25 provides a voltage having a square wave characteristic and this voltage is applied to electromagnet 23 through a conductor 26 and through the common ground connections 27. Thus it will be seen that there is a certain listening time in which the code wheel is allowed to move and when the voltage is applied to conductor 26, indexing wheel 13 is locked in place thus providing a proper code position for interrogation by the optical reading system. Before the electrical pulse applied on conductor 26 is withdrawn, an interrogation pulse is applied to lamp 17 through a conductor 28 and the wave shape is shown generally as a spiked tooth voltage to read the code on the code Wheel only during that period when the index wheel is locked in position. Since optical scanner 22 is sensitive to light,

certain of the circuits connected thereto will be effectively connected to ground 27 and act as a switch in a manner previously described. In other words, certain of the circuits, labeled A, B, C, and D Will be connected to electrical ground 27 depending upon which of the electronic switches are actuated.

As shown in FIG. 1, a four bit code is converted into a decimal and electrical output. This conversion takes place in an electrical circuit having four inputs designated (A, B, C, D) and is completed by using ten transistors having all their emitters connected to each other and to a common impedance connected to the high side of the power supply, and completing the circuits by returning each collector element of each transistor to ground through a separate impedance. Thus, a network is formed that will allow current to flow through only one circuit at a time when unequal voltages are created by grounding certain of the inputs at the code wheel, the inputs being connected to the individual bases of the transistors.

Specifically, ten transistors 30 through 39 are connected so that each of their emitters are connected to a ten volt direct current supply through a resistor 40 and a biasing diode 41. Connected to the bases of transistors 30 through 39 respectively are l0 resistors 50 through 59 and the other terminals of resistors 50 through 59 are connected by a common conductor 42 to the high side of the voltage source which in the present embodiment is ten volts. Connected to the collector of transistors 30 through 39 are 10 resistors 60 through 69 respectively where the other terminals of resistors 60 through 69 Vare connected through a common conductor 43 to electrical ground 27. The output signals are obtained across each of resistors 60 through 69 and are designated outputs 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. Five resistors 70, 71, 72, 73, and 74 have one of their terminals connected to circuit A of the optical scanner 22 and the other terminals are connected respectively to the base element of transistors 30 through 34.

In like manner, three resistors 80, 88 and 89 have one of their terminals connected to circuit B forming a part of optical scanner 22 and the other terminals of resistors 80, 88 and 89 are connected respectively to the base elements of transistors 30, 38 and 39.

In similar fashion, live transistors -92 ,93, 96, 97, and 98 have one of their terminals connected to circuit C which is connected to optical scanner 22 and the other terminals of resistors 92, 93, 96, 97 and 98 are connected respectively to the base elements of transistors 32, 33, 36, 37, and 38.

Circuit D from optical scanner 22 :has one terminal of four transistors 103, 104, 105 and 106` connected thereto and the other terminals of the resistors are connected respectively to the base element-s of transistors 33, 34, 35, and 36.

Operation In order to explain the operation of the circuit, let it be assumed that a code signal alternately provides a light source to the light sensitive element of optical scanner 22 such that circuit A would be rst grounded or have its impedance changed, and then successively circuit C would be grounded and iinally circuit D would be grounded. To help in understanding the explanation of the matrix translator circuit, in FIG. l, below the output designations of through 9, there appears the code designations which will produce the particular output upon grounding of the input at the scanner in that particular electrical circuit. First of all, let it be assumed that all the input circuits are open, that is, there is no light impinging upon any of the light sensitive elements and in this phase of operation, there is no current path to ground for circuits A through D and the base elements of all of the transistors 30 through 39 are at a ten volt potential which is the supply of voltage for this embodiment. Each of the emitter elements will be at a voltage slightly lower that the supply voltage due to the voltage drop across the biasing diode 41 which in this case is indicated as being 0.6 volt. With all of the input circuits A through D remaining open, the outputs from 0` through 9 will likewise have a zero output. Now let it be assumed that circuit A is electrically grounded through the light sensitive element of optical scanner 22 and under this situation, the base of transistor 31 is immediately dropped to one-half the supply voltage because of the equal resistances offered to the flow of current between the supply point and ground since all the resistors in the circuit with the exception of resistor 40 are of equal value and for this particular embodiment equal to 2.2K ohms. Resistor 40 has a value of 470 ohms. 'I'.hus the current is divided by passing through transistor 31 and hen-ce through resistor 61 and passing to ground through the other path formed by resistor 71. The voltages appearing at the base elements of transistors 30, 32, 33, and 34 also drop but to a point that is greater than one-half of the applied voltage due to the other parallel resistance path combinations. Since the voltage level appearing on each of the base elements for transistors 30, 32, 33, and 34 is greater than one-half the supply voltage, these transistors are in a cut off bias state and do not conduct current. Thus the only circuit which is conducting current is that in which transistor 31 is located and consequently an output signal is produced at terminal 1 when the A circuit is closed or electrically grounded. As long as the A circuit is grounded, the base elements of the other transistors which are connected to the A circuit are all electrically above the one-half voltage supply point because of the other current paths which are connected to the power supply.

With circuit A grounded let it now be assumed that code wheel 11 moves so that the A circuit remains grounded by allowing light to impinge upon the light sensitive element and assume that the beam of light impinges upon the light sensitive element connected to circuit C. It will be seen that the base element of transistor 31 remains at the 0.5 Voltage magnitude and the base of transistor 32 ha-s a voltage applied which is less than the 0.5 voltage level of transistor 31. This is occasioned by the fact that resistors 72 and 92 are now connected in parallel and thus have a reduced parallel resistance when compared with the resistance of resistors 52 and 62 connected in series. Since this voltage level drops, the c-ommon emitter line follows the Voltage drop at the lbase element, that is below the 0.5 supply voltage level and this action cuts oi the operation of transistor 31 and the only output current which is now flowing in the circuit is that through transistor 32 and thus a signal is formed across resistor 62 at output number 2.

Assume now that circuits A and C remain grounded by having the light sensitive elements actuated and as code wheel 11 moves further let it be assumed that light impinges upon the light sensitive element of optical scanner 22 so that circuit B is also grounded to terminal 27. In this electrical state, transistor 33 now has resistors 73, 93 and 103 connected in parallel with each other and thus provides a resistive path to the base element of transistor 33 which is approximately 1/3 of that which is connected to the base element of transistor 31 and approximately 1,6 less than that which is connected to the base element of transistor 32. Thus the voltage appearing at the base element of transistor 33 will be lower than `the voltage appearing at any of the other base elements and again, the emitter will follow the lowest base voltage and thus cut off transistors 31 and 32 while maintaining current flow through transistor 33 and resistor 63 to provide an output at terminal 3. Thus it will be seen that in this manner, combinations of four inputs, changing one at a time with a maximum of three being used at one time in this particular circuit provide the necessary outputs for translating the code into a decimal output having 10 discreet units.

It should also be recognized that additional output may be obtained by different combinations of the input circuits and thus in any binary system having four inputs, the total number of outputs could be as high as 16 rather than the decimal outputs shown and described herein. Furthermore, without changing the principle of operation, the number of inputs may be increased or decreased to carry out the teachings of the present invention. Also, it is contemplated that where the output code must go higher than l0 places, a similar arrangement may be used for producing the tens and hundreds digits.

Thus it has been shown that by use of a relatively uncomplicated circuit, a means is provided for changing an input code to a ldecimal output which is unambiguous. Furthermore, in producing the output code it has been shown that where a circuit and code wheel arrangement is used, such as shown, for displaying time and temperature on a sign, that a simplified mechanism has been set forth which teaches how the code wheel may be locked into a reading position so that an unambiguous signal is produced at the output of the matrix translator.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts without departing from the scope of my invention which consists of the matter shown and described herein and set forth in the appended claims.

What is claimed is:

1. An analog-to-digital converter comprising:

(a) code wheel means including detection means having a predetermined code pattern representative of an analog quantity formed on said code wheel means;

(b) condition responsive power means providing rotational movement in accordance with the condition sensed;

(-c) connecting means connecting said condition responsive'power means tosaid code wheel means;

(d) a plurality of equally spaced and radially arranged magnetizable elements, said elements being connected to one of said previously mentioned means;

(e) magnetic means including electrical energizing means disposed in spaced relation from said plurality of magnetizable elements to form an air gap therewith .as said elements pass thereby, said magnetic means developing alternate states of magnetization and non-magnetization to form a magnetic field, having therein, said air gap and at least the closest one of said plurality of magnetizable elements, said magnetic field having a magnitude sufficient to align said code wheel at a code detection position;

(f) and a matrix translator electrically connected .to said Idetection means of said code wheel means, said matrix translator being actuated on N number of input circuits and producing output signals on output circuits equal in number to no more than 2N.

2. The invention as set forth in claim 1 wherein said detection means includes electronic switching means for charging the impedance of said input circuits and wherein said matrix translator includes:

(a) a voltage source of power;

(b) a plurality of transistor stages equal in number to no more than 2N where N equals the number of input circuits, veach of said stages having base, emitter, and collector elements;

(c) a first plurality of impedances, each of which have a pair of terminals, one of said terminals being connected to one terminal of said voltage source of power and the other of said terminals being connected respectively to each of the collector elements of said transistor stages, said output circuits being connected to said pair of terminals of each transistor stage;

(d) N pluralities of impedances each of said impedances of said pluralities having a first terminal connected to only one of said N number of input circuits, the second terminals being connected respectively to a plurality of base, elements of said transistor stages, each of said stages having connected Ithereto at least one impedance different from that connected to all others;

(e) unidirectional impedance means connected between said rst terminal of said voltage source and -said emitter elements of said transistor stages and having a voltage drop thereacross;

(f) and another plurality of impedances having a first terminal connected to the other terminal of said voltage source of power, the second terminals being connected respectively to each of the base elements of said transistor stages, said latter named plurality of impedances forming a plurality of voltages dividers with said N pluralities of impedances upon said detection means changing the impedance of at least one of said input circuits, said transistor stage having the lowest base voltage conducting current therethrough.

3. The invention as set forth in claim 2 wherein, of said N plurality of impedances, no more than 2N impedances of said pluralities have said first terminal -connected to only one of said N number of input circuits.

4. The invention as set forth in claim 2 wherein said first terminal of each of the impedances forming any l/N portion of the pluralities of the impedances are all connected to the same input circuit.

k5. The invention as set forth in claim 2 wherein said detection means includes switching means for changing the impedance of said input circuits and said matrix translator includes:

(a) a voltage source of power;

('b) a plurality of transistor stages equal in number to the mathematical base for which said code is to be translated, each of said stages having base, emitter, and collector elements;

(c) a first plurality of impedances, each of which have .a pair of terminals, one of said -terminals being connected to a ground terminal of said voltage source of power and the other of said terminals being connected respectively to each of the collector elements of said transistor stages, said output circuits being connected t-o said pair of terminals of each transistor stage;

(d) a second plurality -of impedances having a first terminal connected to a first fof said four input circuits the second terminals being connected respectively to a first, second, third, fourth, and fifth base element of said plurality of transistor stages;

(e) a third plurality of impedances having a first terminal connected to a second of said four input circuits the second terminals being connected respectively to said first base element and to a ninth and tenth base element of said plurality of transistor stages;

(f) a fourth plurality of impedances having a first terminal connected to .a third of said four input circuits, the second terminals being connected respectively to said third, fourth, and ninth base elements and to a seventh and eighth base element of said plurality of transistor stages;

(g) a fifth plurality of impedances having a first terminal connected to .a fourth of said four input circuits, the second terminals being connected respectively to said fourth, fifth and seventh base elements and to a sixth base element of said plurality of transistor stages;

(h) unidirectional impedance means connected between said first terminal of said voltage source and said emitter elements of said transistor stages and having a voltage drop thereacross;

(i) and a sixth plurality of impedances having a first terminal connected to the other terminal of said voltage source of power, the second terminals being connected respectively to each Iof the base elements of said transistor stages, said sixth plurality of impedances forming a plurality of voltages dividers with said second, third, fourth, and fifth plurality of impedances upon said detection means changing the impedance of at least one of said input circuits said transistor stage having the lowest base voltage conducting current therethrough.

6. In an analog-todigita1 converter using a rotating code wheel having a predetermined code pattern formed thereon and a detection device used in cooperation therewith, apparatus comprising:

(a) an increment wheel adapted to be rotatably supported, and connected to such code wheel, said increment wheel having a predetermined number of equally spaced and radially arranged elements formed therewith of a highly permeable magnetic material;

(b) condition responsive power means providing rotational movement in accordance with the condition sensed;

'(c) connecting means connecting said condition responsive power means to said increment wheel, at least one -of said means in cooperation with the other of said means having rotational backlash equal to at least one-half the angle subtended by an adjacent pair of said radial elements;

(d) magnetic means disposed in spaced relation from said increment wheel forming an air gap therewith as said elements pass thereby, said magnetic means adapted to be energized and form a magnetic field, having therein, said air gap and at least one of said radial elements in closest proximity to said magnetic means, said magnetic field having a magnitude suicient to align said code Wheel at a code detection position;

(e) and a pulse generator developing square wave voltage pulses and peaked voltage pulses, said square wave voltage pulses energizing said magnetic means for a predetermined period of time thereby stabilizing such code wheel against rotation, each of said peaked voltage pulses being generated during the latter part of the period of time each of said square waves is generated, said peaked voltage pulses energizing such detection device.

References Cited UNITED STATES PATENTS 5/1952 Gridley 340-347 3/ 1961 Petherick 340-347 MAYNARD R. WILBUR, Primary Examiner.

W. I. KOPACZ, Assistant Examiner. 

1. AN ANALOG-TO-DIGITAL CONVERTER COMPRISING: (A) CODE WHEEL MEANS INCLUDING DETECTION MEANS HAVING A PREDETERMINED CODE PATTERN REPRESENTATIVE OF AN ANALOG QUANTITY FORMED ON SAID CODE WHEEL MEANS; (B) CONDITION RESPONSIVE POWER MEANS PROVIDING ROTATIONAL MOVEMENT IN ACCORDANCE WITH THE CONDITION SENSED; (C) CONNECTING MEANS CONNECTING SAID CONDITION RESPONSIVE POWER MEANS TO SAID CODE WHEEL MEANS; (D) A PLURALITY OF EQUALLY SPACED AND RADIALLY ARRANGED MAGNETIZABLE ELEMENTS, SAID ELEMENTS BEING CONNECTED TO ONE OF SAID PREVIOUSLY MENTIONED MEANS; (E) MAGNETIC MEANS INCLUDING ELECTRICALLY ENERGIZING MEANS DISPOSED IN SPACED RELATION FROM SAID PLURALITY OF MAGNETIZABLE ELEMENTS TO FORM AN AIR GAP THEREWITH AS SAID ELEMENTS PASS THEREBY, SAID MAGNETIC MEANS DEVELOPING ALTERNATE STATES OF MAGNETIZATION AND NON-MAGNETIZATION TO FORM A MAGNETIC FIELD, HAVING THEREIN, SAID AIR GAP AND AT LEAST AND CLOSET ONE OF SAID PLURALITY OF MAGNETIZABLE ELEMENTS, SAID MAGNETIC FIELD HAVING A MAGNITUDE SUFFICIENT TO ALIGN SAID CODE WHEEL AT A CODE DETECTION POSITION; (F) AND A MATRIX TRANSLATOR ELECTRICALLY CONNECTED TO SAID DETECTION MEANS OF SAID CODE WHEEL MEANS, SAID MATRIX TRANSLATOR BEING ACTUATED ON N NUMBER OF INPUT CIRCUITS AND PRODUCING OUTPUT SIGNALS ON OUTPUT CIRCUITS EQUAL IN NUMBER TO NO MORE THAN 2N. 